1. Field of the Invention
The present invention relates to a resolver for detecting positional information of a motor, more particularly, to a resolver-excitation signal generating apparatus for generating a reference excitation signal to be supplied to a resolver.
2. Description of the Prior Art
In general, a resolver has been known as a sensor capable of obtaining information relative to a position of a motor only when external reference signal is supplied thereto, from the viewpoint of a mechanical structure. Recently, a motor attached with such a resolver has been employed to control a position of automatic systems, such as a robot, a computer numerical control machine and the like.
Referring to FIG. 1, there is shown a conventional signal generating apparatus for supplying a reference signal to the resolver, described in, for example, U.S. Pat. No. 4,342,077.
Now, the operation of the conventional signal generator will be described in detail.
First, a clock signal having a predetermined frequency generated by an oscillator 1 is supplied to an address decoder 2 which converts the signal having a predetermined frequency into address data of a ROM table 3, for example, such as an EPROM (erasable and programable read only memory). Accordingly, sine and cosine digital data can periodically be output from the ROM table 3 and converted into analog values by means of a digital to analog converter 4. Thus, the digital to analog converter 4 produces the output signal to be supplied to the resolver through a line driver 5.
With the conventional construction as described above, however, there problems that the apparatus is high in price due to an increase in the number of parts such as the address decoder, ROM table, digital to analog convertor etc, and hence maintaining the apparatus is considerably difficult.